1. Field of the Invention
The invention relates to a receiver system of a hearing instrument for operation in the ear canal of a user.
2. Description of Related Art
Typically, receivers (i.e., loudspeakers) of hearing instruments have a geometry (cross-section and length) which makes it difficult to place the receiver deep in the ear canal. The size of the receiver depends on the degree of hearing loss: the more profound the hearing loss of the user is, the larger the receiver has to be in order to generate the required sound pressure levels. In particular, the sharp bend of the ear canal makes it difficult to place receivers deep in the ear canal: even the smallest available receivers can be hardly placed in the region of the sharp bend or beyond it.
A simple reduction of the receiver size would result in a corresponding reduction of acoustic output performance which would not be acceptable. When seeking to maintain the acoustic performance, a smaller cross-section of the receiver would require an increased length which, in turn, would result in a low fit rate due to the sharp bend in the ear canal.
U.S. Pat. No. 4,629,833 relates to a BTE (behind-the-ear) hearing aid comprising two identical receivers, wherein each receiver has a separate sound output channel comprising acoustic impedance elements which serve to adjust the transfer function separately for each receiver. The two sound output channels merge into a common sound channel which is connected to a sound tube extending into the user's ear canal.
European Patent Application EP 1 871 141 A2 relates to a hearing aid receiver system comprising high frequency receiver and a low frequency receiver having a tube connected to its output port, wherein the high frequency receiver is positioned within the tube in a manner that sound emanating from the output port of the low frequency receiver is able to flow around the high frequency receiver. The low frequency receiver, the high frequency receiver and the tube are housed within a housing which is sized to fit within an average person's ear canal.